John II, (born 1398, Medina del Campo, Leon—died 1479, Barcelona) king of Aragon (1458–79) and also king of Navarre (1425–79); he was the instigator of the union of Castile and Aragon through the historic marriage of his son Ferdinand with Isabella of Castile.

John was a younger son of Ferdinand of Antequera, elected king of Aragon (as Ferdinand I) in 1412. John and his brothers retained their positions and revenues in Castile, and he married Blanche, the heiress to Navarre, of which he claimed the kingship (1425–79). On his wife’s death, he married Juana Enriques, daughter of the admiral of castile (1447), whose ambitions led to a conflict between John and his eldest son by his first marriage, Charles, prince of Viana.

In 1458 John succeeded his elder brother Alfonso V as king of Aragon, with Sicily and Sardinia. He was blamed for the mysterious death of his son Charles, who had a strong following in Catalonia, where John’s policies were deeply resented. The Catalans offered the crown to Peter of Portugal, who died, after which they appealed to the French for aid. In October 1469 John arranged for his son by his second marriage, Ferdinand, to marry Isabella, the recognized heiress to Castile, despite the opposition of her brother, Henry IV of Castile. This marriage led to the union of Castile and Aragon and the creation of the modern state of Spain. In Aragon, John’s rule deepened the rift between Aragon proper and Catalonia.

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...the two western Hispanic kingdoms to concentrate on overseas exploration and expansion, and it would not have involved Castile in Aragon’s traditional rivalry with France. The reasons that led John II of Aragon to arrange the marriage of his son and heir, Ferdinand, with Isabella of Castile in 1469 were essentially tactical: he needed Castilian support against French aggression in the...